Bioengineering Seminar Schedule

Fall, 2004 (For prior semesters, click here: Fall 1999, Spring 2000 , Fall 2000 , Spring 2001, Fall 2001, Spring 2002, Fall 2002
Spring 2003, Fall 2003 , Spring 2004 Summer 2004 . Click here to return to current semester)

Friday, September, 3, 12:00 - 1:00, Room 210 Hallowell
"Adhesion Based Approaches for Treating Pathological Inflammation"
Douglas Goetz
Ohio University

Abstract

The adhesion of leukocytes to the endothelium plays a central role in pathological inflammation (e.g. arthritis, inflammatory bowel disease, atherosclerosis). Endothelial cell adhesion molecules (ECAMs) known to participate in leukocyte recruitment (e.g. VCAM-1) are often increased in such settings and contribute to disease progression by virtue of their role in leukocyte adhesion. These observations have led to two potential avenues for the treatment of pathological inflammation. First, there has been an intense effort to develop compounds that inhibit leukocyte adhesion to the endothelium by decreasing ECAM expression. One approach is to use compounds that block pro-inflammatory cytokine (e.g. TNF-a) induced ECAM expression at the transcription level. In collaboration with Dr. Leonard D. Kohn of Ohio University, we have recently identified a derivative of methimazole (a reagent commonly used to treat auto-immune disease), termed C10, that (a) suppresses TNF-a induced expression of VCAM-1 by decreasing levels of the IRF-1 transcription factor and (b) inhibits monocytic cell adhesion to TNF- stimulated endothelial cells. These results suggest that derivatives of methimazole have unique effects on ECAM expression and hold significant potential for the treatment of pathological inflammation. Second, recognition of the increased expression of ECAMs at sites of pathological inflammation has lead to a growing effort to use ECAMs as a means to selectively deliver drugs to sites of pathological inflammation. By exploiting the leukocyte-endothelial cell adhesion chemistry that mediates, in part, leukocyte recruitment to a site of inflammation, we have been able to generate leukocyte-endothelial cell adhesive particles (LEAPs) that selectively and avidly adhere to inflamed endothelium in vitro and in vivo. The LEAPs have adhesion efficiencies similar to that of leukocytes and their interaction with inflamed endothelium can be controlled by particle design. The identification of novel ECAM transcription inhibitors and the potential for targeted drug delivery to inflamed endothelium has significant implications for the improved treatment of an array of pathologies, including cardiovascular disease, arthritis, inflammatory bowel disease and cancer.

Friday, September 10, 12:00 - 1:00, Room 210 Hallowell
William O. Hancock
Penn State University
"Move On Smorgasbord: Recent Kinesin Motor Work from the Hancock Lab"

Abstract

Just like grass-roots politics, kinesin motor proteins are the grass roots movers of the intracellular transport system. We seek to understand their fundamental mechanochemistry and to harness their transport properties for microscale and nanoscale applications in biosensing, biomolecular separations, and the assembly of novel materials. I will discuss recent work from the lab on the fundamental mechanism of the kinesin KIF3A/B, and applied studies on in vitro microtubule organization, microscale transport by kinesins, and pathogen detection strategies.

Friday, September 17, 12:00 - 1:00, Room 210 Hallowell
Melik Demirel
Engineering Science and Mechanics, Penn State University
"Proteins: Simulation, Design and Experiments"

Abstract

Our talk will focus on the elastic network models which describe the proteins motion at equilibrium. Our approach introduces a new concept for classifying building blocks of proteins based on thermal fluctuations. Additionally, we will briefly introduce experimental approaches for design of protein assemblies. Engineered protein assemblies are a new avenue for both biology and materials science applications. Design of protein assemblies requires both experimental and computational approaches. We are developing both experimental methods and simulation tools for the understanding of protein-protein and protein-surface interaction.

Friday, September 24, 12:00 - 1:00, Room 210 Hallowell
Krishnan B. Chandran
University of Iowa
"Fluid-Structure Interaction Simulation of Mechanical Valve Closing Dynamics - Relationship to Thrombus Initiation"

Abstract

Mechanical valves have been used as replacement of diseased native heart valves for more than four decades. Even though patients with implanted mechanical valves lead a relatively normal life, major problems with thrombus initiation and resulting embolic complications are still significant with the currently available mechanical valve prostheses. Patients with implanted valves are required to be under long-term anticoagulant therapy in order to prevent thrombus deposition and its consequences. Recent studies have indicated that the fluid dynamics during the closing phase of valvular function may be responsible for platelet activation and thrombus initiation. Even though in vitro experimental studies have provided valuable information on the effect of flow dynamics and its relationship for thrombus initiation, detailed fluid dynamic measurements in the vicinity of the valve prostheses are not practical with the experimental techniques. Computational fluid dynamic analysis with proper validation provides an opportunity for detailed analysis of the local fluid dynamics with the various mechanical valve geometries. Realistic simulation of the prosthetic valve functional analysis using computational simulations requires the development of a fluid-structure interaction algorithm to predict the leaflet motion due to the hydrodynamic forces acting on the same. This presentation will describe such a simulation and recent results with the analysis of the closing dynamics with a bi-leaflet valve geometry.

Friday, October 1, 12:00 - 1:15, Room 210 Hallowell
Marina Kameneva
University of Pittsburgh

"Effects of Blood-Soluble Drag-Reducing Polymers on Macro- and Microcirculation"

Abstract

Over the past several decades, blood-soluble macromolecules with certain viscoelastic properties, so called drag-reducing polymers (DRPs), have been shown to significantly improve hemodynamics in various animal models when added to blood at nanomolar concentrations. The DRPs have demonstrated many beneficial hemodynamic effects including the ability to increase cardiac output, arterial flow and tissue perfusion without increasing arterial pressure, to reduce lethality of animals after hemorrhagic shock, to increase the density of functioning capillaries in normal and diabetic rats, to enhance myocardial perfusion in an animal model of a coronary stenosis, to significantly increase animal exercise capacity and to prevent lethality caused by exposure to severe hypobaric hypoxia. Chronic intravenous injections of DRPs have been shown to diminish the development of atherosclerosis in several atherogenic animal models. Several synthetic and natural DRPs with chemically dissimilar monomers were shown to produce similar effects in macro- and microvessels. Therefore, the intravascular DRP phenomenon is most likely related to physical properties of the DRPs and not to polymer chemistry.

While the exact mechanisms behind the beneficial effects of DRPs on blood circulation remain to be identified, some hemodynamic and rheological hypotheses regarding the DRP intravascular action were tested. First, it has been demonstrated in vitro that DRPs reduce the size and delay the development of flow separations at vessel bifurcations under flow conditions corresponding to realistic vascular hemodynamics (Kameneva et al., 1990). In vivo, this effect may reduce pressure loss in arterial vessels and thus increase precapillary pressure promoting an increase in density of functioning capillaries and in tissue perfusion which were both observed in animal experiments. Our further hypotheses regarding the mechanisms of the DRP intravascular effects was related to potential impact of the DRPs on red blood cell (RBC) flow behavior in microvessels. The experiments with flow of RBC suspensions in microchannels demonstrated a significant decrease in the near-wall plasma layer due to addition of DRPs to RBC suspensions (Kameneva et al., 2004). This effect may facilitate gas exchange in arterioles and capillaries due to relocation of some RBCs to the near-wall space. In addition, due to an increase in microvessel hematocrit caused by attenuation of the "plasma-skimming" effect, DRPs increase local blood viscosity and wall shear stress potentially promoting the release of vasodilators in microvessels and causing an increase in collateral flow and the number of functioning capillaries.

The drag-reducing phenomenon represents a new bioengineering concept for treatment of insufficient blood circulation and for improvement of resuscitation outcomes from severe blood loss or hypoxia. The beneficial hemodynamic effects of DRPs may find important applications in emergency and cardiovascular medicine and in enhancement of performance. They might also have a significant impact on regenerative medicine.

Friday, October 8, 12:00 - 1:00, Room 210 Hallowell
SPECIAL SEMINAR - WORK IN PROGRESS:
Ahmed Heikal
"Laboratory for Functional Imaging of Biomolecules - An Update"

Peter Butler
"Single Endothelial Cell Mechanotransduction"

Jeffrey Zahn
"New Directions in BioMEMs"

Friday, October 15, 12:00 - 1:00, Room 210 Hallowell
No Classes - Study Day

Friday, October 22, 12:00 - 1:00, Room 210 Hallowell
Min Ho Kim
Penn State University
"Role of Hemodynamic Forces in Smooth Muscle Cell Contraction and Transvascular Filtration In Vivo"

Abstract

A main hypothesis of the current study is that transvascular filtration-induced shear stress might play important roles in endothelial barrier function and SMC contractions.
In the current study performed in vivo and in excised arterioles, interstitial flow-induced shear stress through the vascular wall driven by transvascular filtration was hypothesized to be a mechanical factor that can play a role in the myogenic response in addition to the role of vascular stretch and wall tension. To address this hypothesis, we investigated the relationship between filtration rate (Jv) and the myogenic response by modifying plasma osmotic pressure to attenuate Jv during a step increase in hydrostatic pressure. The myogenic response was attenuated significantly when an osmotic solution of albumin, or albumin plus Ficoll, was infused into the bloodstream to decrease fluid filtration. Moreover, the same inhibition of myogenic tone was found in isolated, cannulated rat soleus muscle arterioles when filtration was osmotically attenuated by intravascular dextran. Taken together, these results are consistent with the hypothesis that shear stress on arteriolar smooth muscle, induced by transvascular fluid filtration, is a contributing factor that helps control myogenic tone.
To understand the role of hemodynamic forces in regulating microvascular permeability, we have investigated effects of acute changes in shear and pressure on endothelial barrier function for water transport. In the study performed in the microvessels of the mesentery, we have obtained evidence that hydraulic conductivity might be regulated via a NO-dependent mechanism in response to acute change in shear rate. Additionally, the effect of sustained changes in pressure on hydraulic conductivity was also investigated using micro-perfusion technique. The substantial increase in hydraulic conductivity was observed following a pressure increase in both small arterioles and venules. It is likely that pressure-induced mechanical stimulus activates a biochemical response that can lead to increase in hydraulic conductivity in response to pressure change. Furthermore, our results suggested that an adaptive sealing effect induced by a step change in pressure also partially contributes to regulate endothelial barrier function. These findings support the idea that endothelial transport barrier responds actively to changes in hemodynamic forces in the microcirculation and regulate transport pathways for water through biological as well as mechanical mechanisms.

Friday, October 29, 12:00 - 1:00, Room 210 Hallowell
Neural Engineering Projects in the Bioengineering Department:
A Bursting Neural Cell Line
Roger Gaumond

Abstract

We have studied the neural discharge behavior of a number of cell lines grown on metal-covered glass surfaces in our lab, and found a neuroblastoma cell line (SK-N-BE(2c)) which exhibits action potential "bursting" activity a few days after plating. This activity becomes increasingly synchronized over a period of one month. Identification of dopamine degradation products in the culture medium suggests that dopaminergic synaptic activity underlies the development of a synchronous firing pattern in these cells. By coating electrode arrays with materials promoting or inhibiting neural cell adhesion and growth, we are developing an in vitro platform for studies of synaptic excitation and inhibition using this bursting cell line.

Brain-Machine Interface
Roger Gaumond and Ryan Clement

Abstract

We are examining schemes for brain-machine interface design using novel neural signal measures applied to microelectrode recordings from motor cortex of rat. We have found that the neural signal energy in small action potential (AP) signals is uncorrelated with large AP signals distinguishable by principle components, and other techniques. We plan to compare the information content of these signal measures by correlating them with the performance of a rat behavioral task. In addition to exploring novel signal processing measures to increase the yield from implanted microelectrodes, we are interested in developing novel strategies for improving the electrode-tissue interface for long-term chronic recording. We will discuss the design constraints of such an interface and offer some thoughts for advancing the state of the art.

Cochlear Implant Studies
Ryan Clement

Abstract

We will conclude our update on neural engineering work currently being pursued at Penn State with one of the more developed neuroprosthetic technologies available today: the cochlear implant. With children being implanted at one year or younger today, it has become an increasing challenge for clinicians to ensure devices are accurately fit based solely on subjective responses from the patient. Specifically, we are interested in exploring the application of stapedius muscle EMG (SEMG) recordings to the objective fitting of cochlear implants. We will provide an overview of progress to date in the development of strategies for obtaining SEMG and provide a glimpse into future work aimed at moving this technique closer to a clinical reality. If successful, this technique would provide the clinician with an effective tool for assessing the auditory system's response to cochlear implant stimulation, provide important information to help in accurate device fitting, and possibly allow for on-line correction of stimulation levels.

Friday, November 5, 12:00 - 1:00, Room 210 Hallowell
Patrick Cirino
Assistant Professor of Chemical Engineering
Penn State University
"Metabolic Engineering in E. coli for the Production of Non-Fermentative Reduced Compounds: Conversion of a Glucose-Xylose Mixture into Xylitol"

Abstract

My talk will start with an update on the practice of "metabolic engineering" from a Chemical Engineer's perspective, including a summary of recent advances and current research directions. This discussion will lead to the contributions my laboratory is making to the field. Lignocellulosic residues from plant biomass are largely composed of carbohydrate polymers, which can be converted into sugar mixtures consisting primarily of glucose and xylose. Our research is aimed at utilizing these sugars as inexpensive sources of energy and carbon backbone for the production of biocatalysts and "renewable" chemicals and fuels through metabolic engineering. We are designing bacteria which divert reduced cofactors (generated through central carbon metabolism) away from native electron transport or fermentation pathways and toward desired heterologous reaction pathways. I will describe a system developed for studying the effects of genetic manipulations on the production of non-fermentative, reduced compounds in E. coli. Our representative electron-accepting reaction is the reduction of xylose to xylitol, a low-calorie, non-cariogenic sweetener used in the food industry. An organism which grows on glucose and "respires" on xylose could be used to refine biomass into xylitol.
E. coli does not naturally produce xylitol, so our first task was to compare the performance of several different xylitol-synthesizing enzymes (xylose reductases and xylitol dehydrogenases) when expressed in this organism. In the presence of glucose E. coli exhibits diauxic growth, in which glucose is preferentially utilized by the cell over other sugars. Genetic modifications allowed for the simultaneous uptake of glucose and xylose and prevented the entrance of xylose into central carbon metabolism. Additional genetic changes and design parameters contributing to increased xylitol production (per glucose consumed) during controlled fermentations will be addressed. Finally, I will discuss future directions of this research, including the use of computational frameworks for metabolic optimization.

Friday, November 12, 12:00 - 1:00, Room 210 Hallowell
Herbert Voigt
Professor, Biomedical Engineering
Boston University
"The Neuronal Circuitry of the Dorsal Cochlear Nucleus - Lessons Learned"

Abstract

This talk will provide an overview of the neuronal circuitry of the dorsal cochlear nucleus (DCN), including anatomy, cell types, physiological response properties in cat and gerbil. References will be made to computational models of the DCN. The specific goal is to understand the role the DCN plays in audition, but a more general goal is to explore lessons leaned by studying a species (gerbil) different from the standard model (cat). It is currently thought that the DCN (in both species) is involved in localization of sounds in the median plane (the plane equidistant from an animal's two ears).

Friday, November 19, 12:00 - 1:00, Room 210 Hallowell
Jeffrey Garanich
Penn State University
"The Role of Fluid Shear Stress in Vascular Smooth Muscle Cell Migration"

Abstract

Elevated levels of vascular smooth muscle cell (SMC) migration and proliferation are widely recognized as hallmarks of intimal hyperplasia (IH). The progression of IH has been attributed to, among other factors, alterations in hemodynamic conditions at the diseased site. Because SMCs are exposed to interstitial flow in intact vessels and direct blood flow in denuded vessels, it is important to determine the effect of flow and its accompanying shear stress (SS) on SMC migration and proliferation. Previous work has shown that increased SS levels inhibit SMC proliferation and that this inhibition is at least in part due to increased production of nitric oxide (NO) by SMCs. The lack of similar reports on the role of SS in SMC migration provides the motivation for this study.
Rat aortic SMCs were seeded onto 8.0 µm pore cell culture inserts that had previously been coated with Matrigel and were then placed into companion plates containing platelet-derived growth factor-BB, which served as the chemoattractant. Cells were subjected to 1-4 hours of 1-20 dyn/cm² SS in a rotating disk apparatus following an initial 6-9 hour incubation. Cells that had migrated through the Matrigel to the underside of the insert were fixed, stained, counted, and compared with static control conditions. ELISA assays were later used to determine the effect of SS on NO and matrix metalloprotainease-2 (MMP-2; a Zn²⁺ endopeptidase involved in degradation of the sub-endothelial intima during SMC migration) production by SMCs. The role of a NOS inhibitor (N^G-nitro-L-arginine methyl ester; L-NAME) in shear-mediated SMC migration, NO production, and MMP-2 activation was also determined. In some experiments, SS was replaced by the addition of a NO donor (S-nitroso-N-acetylpenicillamine; SNAP) or MMP-2 inhibitor. Western blots were conducted to evaluate the role of SS on SMC production of PDGF-AA, another biochemical known to suppress SMC migration.
Four hours of both 10 and 20 dyn/cm² SS significantly inhibited SMC migration and down regulated MMP-2 activity. Four hours of 10 dyn/cm² SS also elevated SMC production of NO. Addition of L-NAME to inserts pre-shear reversed the shear-mediated inhibition of SMC migration, restored MMP-2 activity, and suppressed the increase in NO production. NO (via SNAP) added to inserts inhibited SMC migration and MMP-2 activation. A MMP-2 inhibitor also reduced SMC migratory activity. Western blots showed no effect of 4 hours of 20 dyn/cm² SS on SMC PDGF-AA production.
This study has shown that SS applied directly to SMCs markedly inhibits their migration. This inhibition is due to increased SMC production of NO which down regulates MMP-2 activity. These results correlate well with in vivo observations that elevated flow levels reduce IH.

Friday, November 26, 12:00 - 1:00, Room 210 Hallowell
NO SEMINAR - THANKSGIVING HOLIDAY

Friday, December 3, 12:00 - 1:00, Room 210 Hallowell
Student Presentations:
"Determining the Elastic Modulus of Osteoblasts on Different Surfaces by Atomic Force Microscopy"
by: Joshua Hansen

Abstract

The response of osteoblasts on different surfaces is a key factor when designing appropriate culture conditions in which to grow new bone. Since osteoblasts are sensitive to mechanical forces, the elastic modulus of the cells could be an important property. In this study the elastic modulus of MC3T3-E1 osteoblast-like cells grown on two different surfaces was determined. Cells were grown either on plasma cleaned glass or PS-PBrS (40/60 w/w) demixed polymer films from 2% (w/w) toluene solution. The demixing process results in randomly spaced islands approximately 38nm tall covering about 38% of the surface. The elastic modulus of osteoblasts grown on different surfaces was determined by use of an atomic force microscope with a 5µm diameter sphere attached to the cantilever. The spring constant of the cantilever was first determined in order to control for variation. An array of cantilever position-deflection curves was captured over the cell surface. Using the Hertz model, each curve resulted in an independent measure of the elastic modulus. Averaging the elastic modulus from each curve acquired during four experiments resulted in a value of 9.51 ± 0.085kPa for osteoblasts on the glass surface and 11.9 ± 0.15kPa for osteoblasts on the polymer surface (p < 0.0001). Thus, not only can small differences in modulus be detected, but growing osteoblasts on different surfaces results in significantly different values for the modulus which could affect cell growth under mechanical stimulation.
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"The Role of Gap Junctions in the Response of MC3T3-E1 Clone 14 Osteoblast-like Cells to Oscillatory Fluid Flow"
by: Michael Jekir

Abstract

It is well documented that bone remodels itself as a result of the mechanical loads experienced during use. Bone is a porous material, and subjecting it to mechanical deformation results in the flow of interstitial fluid through its lacuno-canalicular pathways. This fluid flow is sensed by nearby cells, and this engenders signaling cascades that increase bone material production and decrease bone resorption. However, the exact cellular mechanisms at work remain poorly understood, including the method(s) by which cells communicate to effect these changes. Gap junctions, structures that physically connect neighboring cells' intracellular compartments, are one mechanism of cell-to-cell communication. The goal of this study was to investigate the effects of controlled oscillatory fluid flow on MC3T3-E1 Clone 14 osteoblast-like cells. Changes in levels of gene expression and protein production for a number of key proteins known to be involved in osteogenesis were investigated. The experiments were then repeated in the presence of 18b -glycyrrhetinic acid (BGA), a compound known to inactivate gap junctions, in order to determine whether gap junction communication was involved. Of the five proteins investigated, gene expression for osteopontin and osteocalcin was found to be significantly increased 24 hours after a 2-hour period of exposure to fluid flow at a rate sufficient to create a shear stress of 20 dynes/cm² at the cell surface. Our results to date indicate that these increases are not observed in the presence of BGA, which suggests that gap junctions are involved in the signaling process. Western blot data show that levels of secreted osteopontin protein may increase 48 hours post-flow. Further studies will be carried out to determine whether this increase is statistically significant.
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"In Vivo Acute and Chronic Thrombosis Evaluation in a Left Ventricular Assist System"
by: Hanako Yamanaka

Abstract

Left ventricular assist systems (LVAS) provide an alternative to the limited option of a heart transplant for people suffering from cardiac failure. However, thrombosis remains a major limitation to the success of LVAS. As proteins adsorb immediately and coagulation responses may rapidly follow, the acute response of blood to biomaterials is critical. However, the chronic responses that occur as the interface evolves are also of great significance in that LVAS are intended for long-term use (months to years). The varying fluid dynamics of LVAS has also been shown to affect thrombosis and is considered in these studies. Further understanding of the thrombotic response to biomaterials with acute and chronic blood exposure under shear stress is vital to advancement in blood-contacting biomaterials.
In this study, adult 70cc LVAS blood sacs fabricated at The Pennsylvania State University were implanted in bovine models for 3 and 30 days, with and without anticoagulation. A multiscale analysis of thrombosis was performed on the retrieved poly(urethane urea) blood sacs. Gross examination, scanning electron microscopy and confocal microscopy were used to map thrombosis in regions of varied fluid dynamics in the sac.
Results of macroscopic mapping of thrombi by sac location, size, and color were different for acute and chronic studies but not for anticoagulated versus non-anticoagulated groups. Microscopic imaging showed differences in surface topography and adhesion of platelet- and fibrin-like structures between acute and chronic studies and with anticoagulation. Surface topography on both macroscale and microscale in acute and chronic studies also appeared to depend on sac location, which may be due to varied fluid dynamics in the sac. The use of direct immunofluorescent labeling and confocal microscopy provided confirmation of platelet and fibrin adhesion.


Wednesday, December 8, 3:30 - 4:30, Room 210 Hallowell
Wanzhan Liu - Final Defense
Penn State University
RF Magnetic Field, Specific Energy Absorption Rate, and Signal to Noise Ratio in MRI: Experiments and Numerical Calculations with Finite Difference Time Domain Method

Abstract

When MRI moves towards higher fields for higher signal to noise ratio (SNR), one of the challenges is that the complicated interaction between the radio frequency (RF) field and the biological tissues degrades the performance of the system. The finite difference time domain (FDTD) numerical method for electromagnetism, verified by experiments, is a valuable tool to study the RF field in high field MRI. The RF magnetic (B1) field distribution and the SNR for different end-ring/shield configurations in birdcage-type RF coils are examined numerically at 64 and 125 MHz and experimentally at 125 MHz. With the previously developed male body model, a new anatomically accurate female body model is newly developed to study B1 field distribution, SNR, and specific energy absorption rate (SAR) in different body types at 64 MHz and 128 MHz. The RF radiation loss, which is associated with SNR and SAR, in a surface coil, a head size birdcage coil, and a head size TEM coil loaded with phantoms at a frequency range from 64 MHz to 600 MHz is also evaluated numerically. It is found that a) the end-ring/shield configuration in a birdcage coil affects B1 homogeneity and SNR in a head, b) loading a larger, more muscular subject results in significantly less homogeneous distribution, higher RF power deposition, lower SNR, higher SAR levels, and c) the radiation becomes significant at high fields and the interaction between the RF field and the dielectric material in the sample helps to reduce the radiation. These results provide useful information for RF design and MRI safety guide at high fields.


Friday, December 12, 12:00 - 1:00, Room 210 Hallowell
Student Presentations:
"An Automated Single-Cell Electroporation System"
by: Chilman Bae

Abstract

Single-Cell Electroporation (SCE) is an emerging technique used to introduce molecular compounds into micron-scale regions of cells through electric field-induced nanometer-sized membrane pores. Its wide-spread use is limited by the need for specialized electronics and lack of automation. We developed an integrated system of image processing, a motorize micropipette, and programmable electroporation electronics for rapid, automated single-cell electroporation of fluorescent compounds into adherent endothelial cells. Key features include (i) switchable resistance to account for variability of pipette resistance and buffer composition, (ii) software-controlled pulse waveform generation for optimal electroporation of different cell types, (iii) continual monitoring of membrane impedance for quantitative analysis of the electroporation event, and (iv) motorized micromanipulation and image processing for image-based cell selection and automated pipette advancement and pulse timing. This single-cell electroporation system allows rapid, efficient, inexpensive, and non-invasive delivery of minute quantities of fluorescent compounds for subcellular quantitative microscopy.

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"Time Resolved Fluorescence of Stressed Membranes"
by: Ramachandra Gullapalli

Abstract

Cellular mechanotransduction may occur via perturbation of the plasma membrane. However, the precise relationship between membrane tension and lipid dynamics has not been fully explored. We developed a system to study the effects of imposed mechanical stresses on the dynamics of lipids in giant unilamellar vesicles (GUVs). Use of GUVs ensures that membrane chemical composition and the imposed mechanical stresses can be prescribed and tightly controlled. Micropipette aspiration delivers controlled mechanical stresses on artificial membranes containing fluorescent lipids. Multiparameter confocal fluorescence microscopy is used to collect time-resolved fluorescence data of the stressed membranes. Off-line analysis of fluorescence from stressed membranes yields mechanically induced changes in fluorescence diffusion, lifetime and polarization. Such methods allow us to directly test whether physiological membrane tensions are sufficient to alter lipid dynamics, thus providing evidence for a central role for the membrane in mechanotransduction in endothelial cells.

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"Surface Catalyzed Activation of Blood Factor XII"
by: Rui Zhou

Abstract

Development of fully hemocompatible materials remains a substantially unrealized objective of applied biomaterials. Unfavorable cell-and-protein interactions with biomaterial surfaces leading to thrombus (clot) formation are major obstacles that modern surface engineering seeks to overcome. In this pursuit, we find that surface activation of Factor XII, the principal protein reaction initiating plasma clotting, occurs with equal efficiency at hydrophilic and hydrophobic surfaces. However, activation rate is substantially attenuated at hydrophobic surfaces in the presence of plasma proteins. Results help explain why thrombus eventually forms on all materials exposed to blood and offer a new paradigm for the interpretation of hemocompatibility.

For additional information, contact Ms. Doretta Garvey, Dept of Bioengineering, Tel: 814.865.1407 or E-Mail: bioe@engr.Professor, Biomedical Engineering
psu.edu